The research proposed below seeks to understand the genetic and molecular basis of the formation of striated muscle in the growing muscle cell. The study will utilize mutants with abnormal muscle structure to define the genes involved in the assembly process. Through further genetic, ultrastructural and biochemical studies of such mutants an understanding should emerge of how the gene product functions in assembly and how the cell controls the expression of these genes. This approach requires an experimental organism where the problem can be attacked with sophisticated genetic, structural and biochemical analysis and where such mutants are easily obtained. The small nematode Caenorhabditis elegans meets all these criteria. Several mutants have already been found and these have led to the preliminary identification of the structural genes for a myosin heavy chain and paramyosin. This research will concentrate first on identifying precisely both biochemically and structurally the defects in the mutants of myosin and paramyosin. Certain alleles of these genes will be useful in probing the control of gene expression in this differentiated tissue. The gene produce relationship will also be established for other genes where feasible and these in turn will be studied with similar methods. This will require the isolation of new mutants and the identification of additional muscle components. It is hoped that by understanding the molecular genetics of myogenesis in C. elegans general principles will be found which underlie the formation of striated muscle and other organelles common to all higher organisms.